Computational models of an inductive power transfer system for electric vehicle battery charge

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1 Computational models of an inductive power transfer system for electric vehicle battery charge Ao Anele, Y Hamam, L Chassagne, J Linares, Y Alayli, Karim Djouani To cite this version: Ao Anele, Y Hamam, L Chassagne, J Linares, Y Alayli, et al.. Computational models of an inductive power transfer system for electric vehicle battery charge. Journal of Physics: Conference Series, IOP Publishing, 2015, 633 (012010), < / /633/1/012010>. <hal > HAL Id: hal Submitted on 8 Oct 2015 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2 Computational models of an inductive power transfer system for electric vehicle battery charge AO Anele 1,2, Y Hamam 1, L Chassagne 2, J Linares 3, Y Alayli 2, K Djouani 1 1 Dept. of Electrical Engineering, Tshwane University of Technology, Pretoria, South Africa 2 LISV Laboratory, Université de Versailles Saint-Quentin-en-Yvelines, Versailles, France 3 GEMaC Laboratory, Université de Versailles Saint-Quentin-en-Yvelines, Versailles, France aneleamos@gmail.com Abstract. One of the issues to be solved for electric vehicles (EVs) to become a success is the technical solution of its charging system. In this paper, computational models of an inductive power transfer (IPT) system for EV battery charge are presented. Based on the fundamental principles behind IPT systems, 3 kw single phase and 22 kw three phase IPT systems for Renault ZOE are designed in MATLAB/Simulink. The results obtained based on the technical specifications of the lithium-ion battery and charger type of Renault ZOE show that the models are able to provide the total voltage required by the battery. Also, considering the charging time for each IPT model, they are capable of delivering the electricity needed to power the ZOE. In conclusion, this study shows that the designed computational IPT models may be employed as a support structure needed to effectively power any viable EV. 1. Introduction Taking into account high oil prices and environmental awareness, the development of electric vehicles (EVs) is considered as a healthier mode of transportation. This is because the electricity they consume can be generated from a wide range of sources which include fossil fuel, nuclear power and renewable sources (e.g. hydroelectricity, solar power etcetera) [1, 2]. According to [3], it was stated that inductive power transfer (IPT) systems for EV battery charge can be successful if issues such as interoperability between systems of different manufacturers, vehicle design towards effective integration of the inductive charging system, parking guidance and fundamental evaluation of the environmental impacts of the electromagnetic fields are solved. This paper focuses on the aspect of improving the efficiency of the electric power transferred to the on-board battery storage system of EVs. Regarding this aspect, several studies have been presented in [3 7]. Nonetheless, to achieve the aim of this paper, 3 kw single phase and 22 kw three phase computational IPT models for EV battery charge are designed in MATLAB/Simulink and computed based on the technical specifications of the lithium-ion battery and charger type of Renault ZOE. 2. Analysis of IPT Transformer and Effects of Capacitive Compensation The most significant part of IPT systems is its air-cored transformer. Its aim is to provide maximum electric power to the on-board battery storage system of EVs. However, it is faced Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd 1

3 with the problem of weak coupling (i.e., suffers from poor efficiency) due to the relatively large leakage reactances which is associated with its primary and secondary coils. Before presenting the computational models of 3 kw single phase and 22 kw three phase IPT systems, the behaviour of IPT transformer and the effects of applying capacitive compensation are studied based on Figs. 1 and 2. Figure 1. Equivalent circuit of a singlephase IPT transformer. Figure 2. Compensated equivalent circuit. where I P, I M and I S are the primary, mutual and secondary currents respectively, R 1, R 2 and R L are the primary, secondary and load resistances respectively, X L1 and X L2 are the series leakage reactances, X C1 and X C2 are the capacitive reactances and V 1 is the root mean square (RMS) AC voltage. In addition, X M is the mutual inductance between the coils. It is given by 2πfM, where M=k L 1 L 2 ; k is the coupling coefficient, f is the operating frequency while L 1 and L 2 are the series leakage inductances. Based on Fig. 1, the equivalent impedance of the circuit as seen by the AC voltage source is given by Z eq = R 1 + jx L1 + jx MR 2 + jx M R L X M X L2 jx M + jx L2 + R 2 + R L (1) By applying current divider rule, the current division ratio is given by K c = I S I P = jx M R 2 + R L + j(x L2 + X M ) (2) Also, based on Fig. 1, the power transfer efficiency is given by η = R L I 2 S R L I 2 S + R 2I 2 S + R 1I 2 P = R L (R L + R 2 ) + R 1 ( (R 2+R L )+j(x L2 +X M ) jx M ) (3) Amongst other capacitive compensation techniques proposed in [3 5], series-series (SS) technique is employed because it helps to improve the power transfer capability of the transmission line due to its partial compensation of the series leakage reactances. Based on Fig. 2, the equivalent impedance of the circuit as seen by the voltage source is given by Z eq = jx C1 + R 1 + jx L1 + jx M(jX L2 + R 2 + jx C2 + R L ) jx L2 + R 2 + jx C2 + R L + jx M (4) 2

4 For an exactly compensated transmission link of the IPT transformer, the following reactance conditions are vital [4]: X C1 + X L1 + X M = 0 X C2 + X L2 + X M = 0 (5) Thus, substituting (5) into (4) gives the compensated equivalent impedance of the circuit as Z eqc = R 1R 2 + R 1 R L + X 2 M (R 2 + R L ) (6) Based on Fig. 2, the compensated current division ratio is given by K cc = I S I P = Also, the compensated power transfer efficiency is given by jx M R 2 + R L (7) η C = R L I 2 S R L I 2 S + R 2I 2 S + R 1I 2 P = R L (R L + R 2 ) + R 1 ( R 2+R L jx M ) (8) 3. Discussion of Results for IPT Transformer Figure 3 shows the variation of K c and K cc as a function of frequency f for different values of mutual inductance M and resistive load R L. It is obtained by computing equations (2) and (7) in MATLAB M-File. In the case without compensation, the values of K c increase as f increases. However, at higher frequencies, they become constant in spite of the change in R L but, different values of K c are obtained for different values of M. In the case with capacitive compensation, the values of K cc kept increasing as f increases but, different values are obtained for different values of M and R L. The result obtained in Fig. 3 shows that SS capacitive compensation helps to improve the power transfer capability of the IPT transformer (see values obtained for K c and K cc ). In addition, based on the IPT parameters used for MATLAB simulation (see Table 1), the results obtained show that the IPT system considered in [9] must be operated above 100 khz. Figure 4 shows the power transfer efficiency of the IPT transformer with and without SS capacitive compensation. It is obtained by computing equations (3) and (8) in MATLAB. Without compensation, a maximum power transfer efficiency of 78.14% is obtained while with capacitive compensation, 93.18% is obtained. Thus, indicating that with SS capacitive compensation, the power transfer efficiency is increased by 15.04%. Table 1. Parameters for IPT Transformer [8] Physical Parameters Description Values L 1 Leakage inductance of primary coil µh L 2 Leakage inductance of secondary coil µh R 1 Resistance of primary coil Ω R 2 Resistance of secondary coil Ω 3

5 Figure 3. Variation of K c and K cc as a function of frequency f for different mutual inductances M and resistive loads R L. Figure 4. Power transfer efficiency vs coupling coeffiecient. 4

6 4. Computational IPT Models for Electric Vehicle Battery Charge Figures 5 and 6 show the computational models of 3 kw single phase and 22 kw three phase IPT systems for EV battery charge designed using MATLAB/Simulink. Figure 5. 3 kw single phase IPT model. Figure kw three phase IPT model. 5

7 The waveforms of 3 kw single phase AC source voltage, its full wave varying DC voltage and stepped up DC voltage as well as the 22 kw three phase AC source voltage, its full wave constant DC voltage and stepped down voltage are shown in Fig. 7. With a single-phase uncontrolled bridge rectifier (UBR), the AC source voltage (i.e., 220 V ) is transformed to a full wave varying DC voltage. In order to meet the demands of the lithium-ion battery, boost converter is used to produce a stepped up voltage of 400 V as input for the primary full bridge inverter IGBT. Also, with a three-phase UBR, the AC source voltage (i.e., 380 V ) is transformed to a full constant DC voltage and a buck converter is used to provide stepped down voltage of 400 V. Figure 8 shows the waveform of the voltage supplied to the primary coil while Fig. 9 provides a better visibility of the waveform. The single phase pulse width modulation (PWM) (see Figs. 5 and 6) is used to control the switching of the gates of IGBT. Figure 7. 3 kw (a) single phase AC source voltage, (b) full-wave varying DC voltage and (c) stepped up DC voltage. Also, 22 kw (a) three phase AC source voltage, (b) full-wave constant DC voltage and (c) stepped down voltage. Based on the technical specifications given in [9], the IGBT is able to convert the direct voltage of 400 V to a higher and fixed frequency of 40 khz AC voltage. Thus, the primary coil is able to generate a higher frequency electromagnetic field which is then coupled with the secondary coil. Furthermore, in order to guarantee maximum power transfer to the lithium-ion battery, the useful information presented in sections 2 and 3 regarding the application of SS capacitive compensation is incorporated in the designed computational IPT model. Furthermore, the battery charger unit consists of UBR and capacitor filter. This unit is responsible for creating the connection between the IPT system and the lithium-ion battery to be charged. The UBR is used to convert the high frequency AC voltage into a direct voltage while the capacitor filter is added to its output to reduce voltage ripples. 6

8 Figure 8. Voltage supplied to the primary coil. Figure 9. Better visibility of the primary voltage. Figure kw IPT model (a) load voltage, (b) load current, (c) state of charge and (d) discharge characteristics of the battery. The computation of the IPT models given in Figs. 5 and 6 is achieved based on the technical specifications of the lithium-ion battery and charger type of Renault ZOE as presented in [9]. The results (see Figs. 10 and 11) obtained for the load voltage, load current, state of charge of the battery and its discharge characteristic show that the computational models are able to 7

9 provide the total voltage required by the battery. Also, considering the charging time for each IPT model, they are capable of delivering the electricity needed to power the battery of the Renault ZOE. Figure kw IPT model (a) load voltage, (b) load current, (c) state of charge and (d) discharge characteristics of the battery. 5. Conclusion In this paper, computational models of an inductive power transfer (IPT) system for EV battery charge are presented. To achieve this task, 3 kw single phase and 22 kw three phase IPT systems for Renault ZOE are designed in MATLAB/Simulink. The results obtained based on the technical specifications of Renault ZOE show that the IPT models may be employed as a support structure needed to effectively power any viable EV. Reference [1] AO Anele, Y Hamam, Y Alayli and K Djouani 2014 JMMC, 1, [2] AO Anele, Y Hamam, Y Alayli and K Djouani 2014 JMMC, 1, [3] H Barth, M Jung, M Braun, B Schmuelling and U Reker rd European Conference Smart Grids, 1-14 [4] B Schmuelling, SG Cimen, T Vosshagen and F Turki 2012, EPE-PEMC, [5] A Neves, DM Sousa, A Rogue and JM Terras 2011, Power Electronics and Applications Conference, 1-10 [6] M Fareq, M Fitra, M Irwanto, Syafruddin Hasan and M Arinal 2014, J. Phys.: Conf. Series [7] J Lawson, M Pinuela, DC Yates, S Lucyszyn and PD Mitcheson 2013, J. Phys.: Conf. Series [8] S Chopra and P Bauer 2011, 33 rd INTELEC, [9] aspx 8